In the operation of diesel engines utilizing turbochargers embodying intercoolers and/or oil coolers, it is highly desirable that the temperature of the coolant for the engine block remains at a high level while at the same time the temperature of the coolant for the oil cooler and/or intercooler remains at a low level. By maintaining at a high level the temperature of the engine block coolant, the size and/or the cooling air fan power requirements of the radiator can be reduced thereby generally enhancing the operating efficiency of the engine. On the other hand, maintaining a low temperature level of the coolant for the intercooler and/or oil cooler results in significant improvement in the performance of the turbocharger compressor; in the fuel consumption of the engine; and in reducing gaseous emissions from the engine.
To achieve these results, various dual cooling systems have heretofore been provided; however, because of certain design characteristics they have been beset with one or more of the following shortcomings: a) the system was of a complex and costly construction and was susceptible to malfunction; b) it was difficult to maintain the proper temperature differential as to the liquid coolant flowing in the two circuits of the system; and c) the system was ineffective and inefficient in operation.